Some of this sounds very familiar to me. I had a life long friend that I parted ways with around a year ago as she set me up with a girl and then turned on her within a couple of months, constantly talked bad about her behind my back, ruined my 30th birthday, insulted my family, all sorts. In the end she had done so much damage and was so blind to how unacceptable her behaviour was that after we argued very briefly we just never spoke since and I didn't even have to spell it out to her. Rather amusingly she is also with a guy just for what he can provide for her despite very clearly being depressed and unhappy with her life.
Your friend sounds like a horrible person and this entire situation sounds rather childish (other than the fact the friend married a guy who was in a position to leave an estate to her). If you value your girlfriend and her feelings you should probably have cut ties with this friend already. I'm not sure how you are struggling with what to say though. "You show no respect and make no effort with xyz, a person I care about and a true friend wouldn't do that, I want to make things work with her and I can't do so while continuing my friendship with you"
I'm sure her reaction will be entertaining for you but get this toxic idiot out of your life for both you and your girlfriends sake